The tractor pull is one of my favorite obstacles to do and to mention to people. When you say, “then there was the tractor pull” to someone they immediately think you actually pulled a tractor because of how intense a Spartan Race can be. What it actually ends up being is just a chain looped through a cement block. That cement block is often a 4×4 post base, you can buy them at Home Depot – http://www.homedepot.com/p/Unbranded-11-1-2-in-x-8-in-x-11-1-2-in-Concrete-Block-10550005/100350712
The block weighs in the 50 lb. range and is a rough knobby square shape. There is no lighter weight for the women, everyone pulls the same weight. When you get to the obstacle you pick your appropriate block and start dragging it by the chain. You will end up dragging it about 400m through a bumpy dirty course which makes it even more tough when the rough shaped cement block goes in and out of bumps.
One thing to take note of is that when pulling it on downhills it can get some momentum behind it. Be careful when pulling at fast speeds, it can hit you or the people around you.